This invention relates to a hydraulic motor with axial pistons.
In a hydraulic motor of the aforesaid type, a hydraulic operating fluid is fed at a relatively high pressure, which can be of the order of 250-400 atmospheres, to a fixed distribution plate or flange traversed by a central rotatable exit shaft for the motor and facing an axial end of a rotor keyed on to said shaft. Pistons are slidably mounted in bores provided through said rotor, and the axial position of the pistons on the rotor is controlled by a plate facing that end of the rotor farthest from said distribution flange and inclined to the axis of the rotor and therefore of the pistons. These latter are disposed with one of their ends in contact with said inclined plate, such that at any moment during the rotation of the rotor, one half of the pistons is moving away from said flange, while the other half is moving in the opposite direction. Said pressurized fluid acts on the pistons which move towards the inclined plate and which, by cooperating with this latter, cause the rotor to rotate, said fluid being fed through said distribution flange to a front groove therein facing the rotor and constituting a feed header extending over substantially one half of the rotor. The other half of the rotor contains an analogous discharge header to which is fed the fluid leaving the rotor by the effect of the pistons which move towards the distribution flange.
In one particular known hydraulic motor of the aforesaid type, said axial bores or cylinders in the rotor communicate with said feed and discharge headers by way of a rotating distributor constituted by a disc comprising axial appendices on one side which engage in a sealed manner inside said cylinders, and a flat surface on the other side which is arranged to cooperate frontally in a sealed manner with an analogous flat surface provided on said distribution flange, and in which said feed and discharge headers are provided. These latter communicate with the cylinders via axial bores provided through said disc and said appendices.
In general, the proper construction of said rotating distributor requires that two conditions be satisfied at the same time, namely that the said two flat surfaces of the distributor and distribution flange must be perfectly parallel to enable the pressurized fluid to pass therebetween only in the quantity necessary for hydrostatically supporting the rotating distributor with respect to the distribution flange, and the said appendices must engage in the relative cylinders in a perfectly sealed manner. When the normal operating pressure is considered, together with the fact that the position of the axis of the rotor, the rotating distributor of which is angularly rigid with said appendices, is defined relative to the distribution flange by a kinematic chain comprising said central shaft and generally two or more radial bearings, it is immediately obvious that extremely high machining precision is required to simultaneously satisfy the said two conditions, and in the case of rotor diameters exceeding a certain value, this results in commercially unacceptable manufacturing costs.